title: Cellular neurothekeoma with fascicular growth features mimicking cellular dermatofibroma.
abstract: BACKGROUND
  Cellular neurothekeoma (CNT) is a benign cutaneous mesenchymal neoplasm. Most demonstrate a lobulated to micronodular architecture. Rarely, CNT demonstrates a predominantly fascicular growth pattern, without prominent sclerosis and thus can mimic cellular dermatofibroma (DF).
  
  
  METHODS
  Three CNT with a predominantly fascicular pattern were obtained. The clinicopathologic features and accompanying immunohistochemical stains were evaluated.
  
  
  RESULTS
  All cases demonstrated a moderately cellular proliferation of epithelioid to spindle cells with pale to eosinophilic slightly granular cytoplasm, vesicular nuclei, and a single nucleolus arranged in a fascicular pattern with thick collagen bundles at the periphery (collagen trapping). One case had prominent epidermal hyperplasia. The neoplastic cells expressed NKI-C3, CD10, and micropthalmia transcription factor and lacked expression of factor XIIIa, S-100, epithelial membrane antigen, and CD34.
  
  
  CONCLUSIONS
  Our cases showed an unusual pattern of CNT with a predominantly fascicular growth pattern, thickened collagen bundles at the periphery, and occasionally epidermal hyperplasia. The overlap with cellular DF is striking. The presence of plump to epithelioid cytomorphology with abundant cytoplasm, with focally prominent nucleoli; the presence of focal lobulated to micronodular growth pattern along with micropthalmia transcription factor positivity; and lack of factor XIIIa expression are helpful in distinguishing fascicular CNT from cellular DFs.
authors.affiliation: Department of Pathology, Northshore University HealthSystem, Evanston, IL 60201, USA.
authors.forename: Beenu
authors.initials: B
authors.lastname: Thakral
authors.forename: Briana C
authors.initials: BC
authors.lastname: Gleason
authors.forename: Antoinette B
authors.initials: AB
authors.lastname: Thomas
authors.forename: Steven D
authors.initials: SD
authors.lastname: Billings
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Victor
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Cibull
mesh_terms: D000328:Adult; D003937:Diagnosis, Differential; D005260:Female; D018219:Histiocytoma, Benign Fibrous / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008875:Middle Aged; D018321:Neurothekeoma / Q000378:metabolism / Q000473:pathology*; D012878:Skin Neoplasms / Q000378:metabolism / Q000473:pathology*